The present disclosure relates to a direct current power generating system, and more particularly, to a resolver error compensation technique of a PMG-based direct current power generating system and method of operating.
Permanent magnet synchronous generators (PMG) are used in electric power generating system for electric or hybrid-electric vehicles. A generator control unit (GCU) is used to convert variable alternate current (AC) voltage at the output of the PMG into constant direct current (DC) voltage to supply vehicle loads. GCU contains a pulse-width modulate (PWM) converter (i.e. active rectifier) that may require accurate information about PMG rotor angular position for proper commutation of active rectifier switches.
Rotor angle may be detected by a resolver. In high power density applications, the PMG (with a high number of poles) coupled with a frameless two pole resolver may be used. Output of the resolver may be an electrical signal that corresponds to rotor angle. Resolver outputs may be sine and cosine analog signals that, when provided to a resolver-to-digital converter (RDC) may produce a digital output corresponding to the rotor's absolute angular position.
Various sources of angle error in the output signal of the resolver may include mechanical misalignment, electrical characteristics and conversion time errors. These errors with a multi-pole PMG may significantly aggravate accuracy of electrical angle that should be within at least one degree to obtain good control of the power generating system. Field oriented control of an active rectifier coupled to the PMG may not be accurately implemented over the entire speed range without knowing the actual position of the PMG rotor. It is therefore desirable to compensate resolver output error caused by misalignment and electrical sources of error.